1. Field of the Invention
The present invention relates to a viewfinder apparatus and an optical instrument having the viewfinder apparatus, and in particular relates to a viewfinder apparatus in which, for example, an optical viewfinder (OVF) and an electronic viewfinder (EVF) are switchable so that a selected image from one of the finders can be observed in a visual field. The viewfinder apparatus is suitable for use in cameras, video cameras, electronic still cameras, and so forth.
2. Description of the Related Art
Hitherto, various types of viewfinder apparatuses have been proposed for optical instruments such as film cameras and video cameras.
For example, an Albada finder and a mark-type finder are well-known, so-called virtual image type finders, in which a virtual image is formed by an objective lens so as to be observed via an eyepiece.
FIG. 3 is a schematic view of essential parts of a conventional mark-type finder; the drawing shows an objective lens 11 having a negative refracting power, an eyepiece 12 having a positive refracting power, a field frame 13, a mirror 16, a target lens (a target lens optical system) 15, and a half mirror 14.
When observing an object, an inversed Galilean type finder comprising the objective lens 11 and the eyepiece 12 is used. A light ray passing through a transparent portion of the field frame 13 is reflected by the mirror 16 and is concentrated by the target lens 15 so as to be introduced to the eyepiece 12 via the half mirror 14, thereby being superimposed on a virtual image of the object.
The target lens 15 serves to eliminate a sense of incongruity of an object visibility through the finder by causing an image in the field frame 13 to have a predetermined visibility. In the vicinity of the center of the field frame 13, a display such as a distance-measuring mark may be provided.
In a viewfinder apparatus, a liquid crystal display element is used as a display of a finder field frame (field frame), as disclosed in Japanese Patent Laid-Open No. 7-43781, U.S. Pat. No. 5,581,318, and Japanese Patent Laid-Open No. 9-265120, for example. Ambient light rays are normally utilized as a light source thereof in a mark-type finder.
In Japanese Patent Laid-Open No. 10-20385, a mark-type finder is proposed in which a liquid crystal display element has a back light device, and the field frame is displayed by back-lighting due to the back light device.
On the other hand, in video cameras, etc., a so-called EVF (electric viewfinder) is in general use, in which an image of an object is formed in an image pick-up element such as a CCD in an image pick-up system and image information is displayed in a liquid crystal display element by using an electric signal from the image pick-up element so as to be observed through the viewfinder system.
In the above-mentioned EVF as a viewfinder apparatus, an observed finder image is a picked-up object image itself, so that it has a merit of having no parallax. In contrast to this, however, considerable electric power is required for driving the liquid crystal display element. In optical instruments such as electronic still cameras, since the compactness thereof is important, reduction in capacity of a battery equipped in the instrument is required. In video cameras, an ordinary optical viewfinder (OVF) other than the EVF is also used.
In an optical instrument having both the EVF and OVF, since an optical viewfinder is independently constructed separately from a liquid crystal display element for the EVF, a large space is needed and the efficiency in space savings is also low, so that the size of the entire apparatus is prone to increase.
Accordingly, it is an object of the present invention to provide a viewfinder apparatus and an optical instrument using the apparatus in which space is efficiently used, enabling the entire apparatus to be miniaturized, and the apparatus is switchable between modes of an OVF and an EVF.
In order to achieve the above object, in accordance with a first aspect of the present invention, there is provided a viewfinder apparatus comprising: an objective lens unit; an eyepiece unit; an image display element for displaying an image formed by an image pick-up element; an illuminating device for illuminating the image display element; an optical system for introducing light backward from the image display element which is illuminated by the illuminating device; and a reflecting member for introducing light from the optical system to the eyepiece unit, wherein the values of a focal length fr of the optical system and a focal length fe of the eyepiece unit satisfy the condition 1 less than fe/fr less than 6.
Preferably, the reflecting member is arranged between the objective lens unit and the eyepiece unit and is rotatable about a predetermined axis.
It is preferable that in the optical system, the viewfinder apparatus be switchable between a case in which observation of a luminous flux from the illuminated image display element as the image via the eyepiece unit is provided by reflecting the luminous flux at the reflecting member, and a case in which observation of an image formed by the objective lens unit via the eyepiece unit is provided by moving the reflecting member from an optical path between the objective lens unit and the eyepiece unit.
The apparatus may preferably further comprise a shielding member which is insertable into and detachable from an optical path between the objective lens unit and the reflecting member, and wherein the reflecting member may be a half mirror.
Preferably, the shielding member is arranged between the objective lens unit and the half mirror, and wherein the viewfinder apparatus is switchable between a case in which observation of a luminous flux from the illuminated image display element as the image via the eyepiece unit is provided by reflecting the luminous flux at the half mirror, and a case in which observation of an image formed by the objective lens unit via the half mirror and the eyepiece unit is provided by moving the shielding member from an optical path between the objective lens unit and the half mirror.
The optical system may preferably be a target lens optical system for magnifying a luminous flux from the illuminated image display element as an image.
Preferably, the target lens optical system has a face having a negative refracting power.
In order to achieve the above object, in accordance with a second aspect of the present invention, there is provided a viewfinder apparatus comprising: an electric viewfinder for observing a luminous flux from an illuminated image display element for displaying an image formed by an image pick-up element as the image via a predetermined optical system and an eyepiece unit; and an optical viewfinder for observing an image formed by an objective lens unit via the eyepiece unit, wherein the electric viewfinder and the optical viewfinder are switchably used, and wherein the values of a focal length fr of the optical system and a focal length fe of the eyepiece unit satisfy the condition 1 less than fe/fr less than 6.
Preferably, a rotatable reflecting member is arranged along an optical path between the objective lens unit and the eyepiece unit, and wherein the electric viewfinder observes a luminous flux from the illuminated image display element as the image by reflecting the luminous flux at the reflecting member while the optical viewfinder observes an image formed by the objective lens unit by moving the rotatable reflecting member from the optical path.
Preferably, a half mirror is provided along an optical path between the objective lens unit and the eyepiece unit and an insertable and detachable shielding member is provided along an optical path between the objective lens unit and the half mirror, and wherein the electric viewfinder observes a luminous flux from the illuminated image display element as the image by reflecting the luminous flux at the half mirror while the optical viewfinder observes an image formed by the objective lens unit via the half mirror by moving the shielding member from the optical path.
An optical instrument may preferably comprise a viewfinder apparatus according to the first aspect of the present invention and the image pick-up element for forming an image of an object via an image pick-up optical system.
An optical instrument may preferably comprise a viewfinder apparatus according to the second aspect of the present invention and the image pick-up element for forming an image of an object via an image pick-up optical system.
According to the present invention, a viewfinder apparatus and an optical instrument using the same can be achieved, in which the entire apparatus can be miniaturized and the OVF and the EVF are switchable.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.